As the digital contents have become prevalent, the infringement on their copyrights by illicit copying has given birth to a social problem. In analog recording to a tape medium, audio or video data are recorded in an analog manner and so copying of the data will result in a lower quality. In digital data recording or reproduction, however, a digital data recorder/player can be used to repeatedly copy audio or video data many times with no quality degradation, in principle.
Thus, the loss due to such illicit copying has become greater in the field of digital recording/reproduction than in the analog field, and thus it has become very important to prevent illicit copying with any digital recording/players.
To solve the above problem, it has been proposed to add copy-control information to digital contents and use the added information in order to prevent illicit copying of the digital contents.
For example, the copyright protection method employing a generation-limiting copy control called “SCMS (serial copy management system) is applied to digital data recorder/players for CD (compact disc), MD (mini disc; registered trademark), DAT (digital audio tape), etc. The SCMS copy-control method is to authorize to copy an audio content once but inhibit any further copying of the thus once copied audio content.
The SCMS copy-control method will be described in detail below with reference to FIG. 1.
For example, it is assumed here that a disc 1 has original-source audio signals digitally recorded therein. The digital audio signals are recorded in a predetermined recording format in the disc 1, and there is recorded in a specific area in the digital signals additional information indicating that the SCMS copy-control method permits to copy the digital audio signals only once.
A disc player 2 plays back the disc 1 to reproduce the digital audio signals from signals read from the disc 1, and sends the digital audio signals along with the additional copy-control information to a disc recorder 3. For sending the digital audio signals to the disc recorder 3, the disc player 2 will normally take a length of time equal to the time taken for reading the signals from the disc 1 (at the same speed).
Receiving the digital audio signals, the disc recorder 3 recognizes, when the information added to the audio signals indicates that the received digital audio signals may be copied only once, that the input digital signals can be copied. The disc recorder 3 will record the digital signals as a copy to another recordable disc 4. In this case, the disc recorder 3 rewrites the additional information from “one copy allowed” to “further copy inhibited”. Thus, the digital signals as the copy and also the additional information “further copy inhibited” are recorded or copied to the disc 4.
In case the digital audio signals thus recorded as the copy in the disc 4 (first-generation disc) are read from the disc 4 played in another disc player 5 and supplied to another disc recorder 6, however, since the disc recorder 6 will detect that the additional information included in the digital signals is “further copy inhibited”, the digital audio signals cannot further be recorded to any recordable disc 7.
In this case, the copying speed is equal to that at which the audio signals have been sent from the disc player 2. That is, if a standard playback time is taken for reproduction of the audio signals, the copying speed will be equal to a normal playback speed.
The “standard playback time” is a real-time playback speed for audio signals, namely, it is a playback speed at which audio signals can be perceived by the person having the ordinary ability of hearing. For example, the standard speed for reproduction of data depends upon each player and is independent of the human perception.
As above, the SCMS copy-control method protects the copyright of data by permitting a first-generation copying in a recorder while inhibiting a second-generation copying from the first-generation copy.
The SCMS method is intrinsically intended to prevent copyrighted data from being copied in a large amount for unauthorized commercial distribution, rather than to inhibit such a second-generation copying. Therefore, it is not negative against the currently prevailing copyright concept that “free copying within a range of private use”.
Recently, a variety of recording/reproducing media such as an MD (mini disc; registered trademark) player, card-type memory player incorporating a semiconductor memory, etc. have been commercially available. Thus, users can selectively use the MD player, card-type memory player or the like as a playing medium as they currently like. In these circumstances, copying is frequently done by the use of any of the above players, and the SCMS copy-control method allowing to copy data only from an original medium will be inconvenient even for copying of the data only for private use.
Many of the recent personal computers are provided each with a CD playing function to store (copy) musical information distributed via a CD into a hard disc in a hard disc drive built in the personal computer and reproduce the musical information from the hard disc. Copying to the card-type memory player can be effected at such a high speed that copying from the hard disc in the personal computer will be more convenient. More precisely, copying from the hard disc to the card-type memory player provides a second-generation copy while musical information stored in the hard disc cannot be copied to the card-type memory player.